Transformer



Dec. 29, 1925' 1,567,844

A. B. HENDRICZKS, JR

TRANSFORMER Filed Nov. 10, 1921 Inventor":

Patented 'Dec. 29, 1925.

UNITED STATES ALLAN B. HENDRICKS, JR.., 0F PITTSFIELD, MASSACHUSETTS, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

TRANSFORMER.

Application filed November 10, 1921, Serial No. 514,328.

To all whom it may concern:

Be it known that I, ALLAN B. HENDRICKS, Jr., a citizen of the United States, residing at Pittsfield, county of Berkshire, State of Massachusetts have" invented certain new and useful Improvements in Transformers, of which thefollowing-is a specification. 7

My invention relates to electrical transformers. For some purposes, a source-of current at veryhigh potential is desirable, this being especially true in connection with the testing of high tension insulators, the investigation of corona effects on high tension transmission lines and various other theoretical investigations. The present invention therefore relates more particularly to transformers adapted to be used under circumstances requiring the production of current at very high potentials.

A single transformer designed to deliver currentvat very high potential is expensive and bulky because of the large amount of in sulation' necessary and the considerable spacing and consequent large amounts of other material required becauseof the high potential differences at which various parts of the transformer must be operated. It has been suggested that this difficulty be overcome by the use of a plurality of transformer units with their high tension terminals connected in series, each unit being sep arately excited and all except the first one being insulated from the rimary source of current and from ground y one or more insulatingtransformers. This method is objectionable because of the expense and the inconvenience of handling the large number of units. Another method suggested has been the use of a plurality of auto-transformers connected in series, but the very high reactance ofsuch a system makes it of little value for most purposes.

The main object of the present invention is to overcome the disadvantages of the arrangements which have heretofore been suggested bythe use'of a plurality of transformer units connected in series, the first unit being preferably excited directly from some suitable source of current and each of the higher units being excited by means of exciting windings which are structurally combined with the next unit below but which operate inde endently of the main windings of the trans ormer unit with which they are structurally associated. Another object of the invention is to provide means for protecting the windings from destructive effects due to high frequency oscillations caused by disturbances in the circuit fromthe breakdown of insulation under test, sudden short circuits, or other sudden changes in circuit conditions.

Other objects and advantages will appear from the following description taken in connection with the accompanying drawing, in which Fig. 1 indicates the construction and arrangement of parts where two transformer units are used in accordance withthe present invention, a portion of each unit being broken away to reveal the arrangement and connections of the windings and the means already referred to for protecting them against high frequency oscillations, and Fig. 2 is a diagram of the arrangement of the windings and their connections in the two units.

Like reference characters refer to similar parts in both figures of the drawing.

ln'the embodiment of the invention revealed in the drawing, the system comprises two transformer units 1 and 2 so connected that the terminal voltage of the system will equal the vector sum of the individual voltages of thetwo units. It will become apparent as the description proceeds that the reactance of such a system is very low as compared, for instance, with the reactance of an auto-transformer system, and that therefore the terminal voltage of two units connected in series is substantially equal to the arithmetical sum of the individual voltages of the units. It will further be apparent that additional units may be added in order to develop greater terminal voltage until the number of units is such that their combined reactance causes the vector sum of the individual voltages to differ so much high voltage winding 6. These two windings have their lower ends connected by a conductor 7 which is connected to the casing 3. The upper end of the low voltage winding 5 of the first unit is connected by a conductor 8 to one terminal of the source of current 9 and the casing 3 of this first unit is connected to the other terminal of the source of current by a conductor 10, so

that this low voltage winding is adapted to be excited directly by the source of current.

Upon the leg 4 of the core, there is also wound a primary winding 11 and a secondary winding 12. Thesemay be called exciting Windings as their purpose in each unit is to furnish current for exciting the main primary and the primary excitin winding of the next unit above. The primary exciting winding 11 is connected in ,parallel with the main primary winding 5 and each of them windings has the same number of turns as they are both wound upon the same core and have the same po tential applied across their terminals. The

- volts or more, between its terminals, the potential difference between the terminals of each of'the three windings 5, 11 and 12 is comparatively low, perhaps something like a thousand volts.- The secondary exciting winding 12 therefore has its turns concentrated near theupper end of themain high voltage winding 6 since it must be insulated therefrom at its lower end. The turns of the primary exciting winding 11 are also concentrated near the upper end of the main windings 5 and 6 and under the secondary exciting winding 12 so that the two exciting windings 11 and 12 may be in good inductive relation to each other. The lowor end of the secondary exciting winding 12 and the upper end of the main secondary winding 6 are bothvconnected to a conductive protective shield 16 which will be described later. The potential of 511 parts of the winding 12 is therefore far above that of the lower end of the main secondary winding. All parts of the primaryexciting winding 11 however are at very much lower'potential as this winding is 1n parallel connection with the main low voltage Winding 5. The windings 5 and 11 are therefore well insulated from the windings 6 and 12 by a suitable insulating barrier 13.

The upper or high voltage terminal of the main secondary winding 6 is connected to a connected by an insulated conductor 16 carried inside the tubular conductor 14 to the upper ends of both the main primary winding 5 and the primary exciting windin 11 of the next unit above. It will be obvious that with the connections which have been described, the secondary exciting winding 12 of each unit is connected across the terminals of both the main primary winding 5 and the primary exciting winding 11 of the next unit above so as to furnish exciting current for these two windings. These two windings 5 and 11 in each unit induce current in their respective secondary windings 6 and 12. The-purpose of connecting the lower end of the secondary exciting winding 12 to the protective shield 16 and thence through the tubular conductor 14 and the casing 3 of the next unit to the lower ends of the two primary windings 5 and 11 of this next unit is to avoid the use of a separate conductor between these points. It is obvious that such a separate conductor may be used if desired, in which case the connection 7 between the lower ends'of the primary windings 5 and 11 and the lower end of the main secondary winding 6 may be omitted.

The transformer units have been described as being similar in construction and arrangement of parts but they may be connected together in a variety of difierent ways. As shown in Fig. 1 of the drawing, the casing 3 of the first unit is connected to the ground 17, this connection also serving to complete a path to ground from the lower end of the main or high tension secondary winding 6 of this first unit. There is therefore a c ntinuous series path from the ground 17 rough the main secondary winding 6 and tubular conductor 14 of the first unit and the casing 3, main secondary winding 6 and tubular conductor 14 of the second unit to the high voltage terminal 18 ot' the system. The total potential difierence between the upper terminal of the system and its lower terminal or ground will be the vector sum of the potentials generated in the high tension windingsof the individual units audit is obvious that an extremely-high terminal voltage may be attained by the use of additional units, its practical maximum limit being determined only by the combined reactances of the individual units as already explained and by the insulation provided between the higher units and ground. As indicated in Fig. 1 of the drawing, the casing of the lower unit is of their inductance..-

grounded and does not need to be insulated from the ground. .The casing of the second unit, however,'is at a potential equal to that of the upper high tension terminal of the lower unit and must be correspondingly insulated from ground as by mounting it upon an insulating stand 19. The casing of each unit must be insulated from ground for a potential difference equal to the combined potential of the other. units between this one and the ground terminal of the system.

It will be apparent that in the last unit of the system, the primary and secondary exciting windings lland 12 are idle as their only purpose is 'td excite an additional unit in case one may be found desirable at any time. It will also be apparent that these two exciting windings operate entirely independently'of the main transformer windings and 6, and are associatedwith them on the same core merely for purposes of economy in construction and not to create any transfer of energy between the two sets of windings.

During the operation of a high tension system such as has been described. there frequently occur sudden disturbances in the high tension circuit due to such causes as sudden short circuits, and the breakdown of insulating material which is being subjected to high potential tests. As is well known to those familiar with electrical phenomena, such a disturbance in the exterior testing circuit-may cause an oscillating current of very high frequency and at potentials far in excess of the normal potential at which the system is designed to operate to enter the upper unit at its-terminal As this high frequency current reaches' the end turns of the high tension winding, itmay produce excessively high potentials between the turns because The protective shield '16 is therefore provided between the winding 12 and the upper turns of the .winding. 6. This shield is in the form of a cylindrical member composed of conductive material. It is of considerable depth or width at that portion of the windings directly under the connection between the high tension winding and the high tension terminal as the greatest protection is .obviously necessary at this point. The depth or width of the shield decreases in each direction from this point along the turns of the windin and therefore away from the point at w ich destructive high frequency oscillating disturbances may enter the windings- The shield is split at the side opposite this point in order that it may not form a short circuited conductor to interfere by its reactance with the flow of magnetic flux in the core. -Without this shield, the closely wound turns of the windings act as condenser plates and there is also a considerable capacity outwardly between these turns and the transformer casing and also inwardly between these turns and the transformer core. A high frequency high tension current coming in through the terminal would penetrate the turns through these condenser paths, and as some current would leave each turn through the lateral paths, it is obvious that the currents in the upper turns would be very high and would cause the potentials between the first few turns to reach such excessive values as to cause seriousinjuryto the winding. This injurious effect is prevented, however, by the shield which-has been described. The shield is instantly brought to the potential of any dangerous oscillating venting flow of current through the capacity of the turns and consequently preventing any excessive differences of potential between these turns. This electrostatic efi'ect decreases gradually with the distance from the terminal so that there may be no abrupt change in the efi'ect on the turns at its lower edge, this gradual decrease being due to the varying depth of the shield. In securing this gradual decrease in the electrostatic effcct, it is preferred for structural reasons to vary the depth of the shield as shown rather than to vary its distance from the turns.

What I claim as new and desire to secure by Letters Patent of the United States, is,-

' 1. In a transformer, a magnetic core, main primary and secondary windingssurroundmg the core, a second secondary winding surrounding the core, and a second primary winding in good inductive relationship with the second secondar winding, the

turns of the second secondary end of the second primary windings being concentrated near one end of the main secondary winding.

2. In a transformer, a magnetic core, main primary and secondary windings surround- 1 mg the core, a second secondary winding surrounding the core with its turns concentratcd near one end of the main secondary winding, and a second primary winding with its turns concentrated near one end of the main primary winding and in good inductive relationship with the second secondary winding.

3. In a transformer, a magnetic core, main primary and secondary windings surrounding the core, a second secondary winding surrounding the core, a second primary winding surrounding the core, the second secondary and primary windin s being between the main secondary an primary windings, and a conductive shield between the two secondary windings and connected to the high tension end of the main secondary winding.

4.. In a transformer, a magnetic core, main to the high tenslon end of the main sec-- ondary winding, said shield varying in width along the main secondary WlIldlIl". 5. In a-transformer, a magnetic core, a

primary and a secondary winding surrounding the core, and a conductive shield between sald two windings and connected directly to the high tension endof the secondary winding.

6. In a transformer, a magnetic core, a primary and a secondary winding surrounding the core, and a conductive shield between said two windings and connected directly to they high tension end of the secondary winding, said shield varying in width along the secondary winding.

f 7. In a transformer system comprising two transformer units, a magnetic core in each unit, main primary and secondary windings surrounding each core, a second secondary winding and a second primary winding surrounding each core, the two primary windings in the second unit being connected in parallel and across the second secondary winding of the first unit, and means for exciting the two ings of the first unit.

8. In a transformer system comprising two transformer units, a magnetic core in each unit, main primary and secondary windings surroundingeach core, a second secondary winding and. a second primary winding surrounding each core, the second secondary and the second primary winding in each unit being concentrated near one end of the main secondary winding in the same unit, the two primary windings in the second unit being cennected in parallel and across the second secondary winding of the first unit, and means for exciting the two primary windings of the first unit.

9. In a transformer system comprising a plurality of transformer units, a magnetic core in each unit, and main primary and secondary windings surrounding each core, said secondary windings being connected in series, at least one of said cores having a second secondary winding and a second primary winding concentrated near one end of its main secondary winding, each of said second secondary windings being connected to supply primary exciting current to an adjacent unit.

In witness wheerof, I have hereunto set my hand this 8th day of Nov 1921.

ALLAN B. HENDRICKS. Jn.

. Certificate of (lorrection;

It is hereby certified that in Letters Patent No. 1,567,844, granted December 29, 1925, upon the application of'Al-lan B. Hendricks, jr., of Pittsfield, Massachusetts, for an improvement in Transformers, an error appears in the printed specification requiring correction as follows: Page 3, line 106, claim. 1, for the word end read and; and that the said Letters Patent should be read with "this correction therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 15th day of June, A. D. 1926.

. M..J'. MOORE, Acting Commissioner of Patents.

primary wind 

